帘线钢小方坯82A铸坯表面和内部缺陷分析

帘线钢的表面裂纹缺陷和中心偏析是影响铸坯质量的关键因素。采用了铸坯表面宏观缺陷分析、裂纹微观形貌表征、Gleeble高温力学性能、中心偏析等检测手段,对帘线钢82A断面150 mm×150 mm小方坯在稳态和非稳态浇铸条件下,铸坯表面和内部质量缺陷进行了分析。结果表明,铸坯振痕间距为13 mm,角部出现振痕紊乱;非稳态铸坯表面振痕波谷和凹坑处均发现了明显的横裂纹,而稳态样品则未见明显的表面横裂纹。铸坯内部沿着中心缩孔有长约55 mm中心裂纹,铸坯平均中心碳偏析指数达到1.09。根据该钢种的高温力学性能并结合裂纹形貌分析,非稳态下铸坯表面易冷却不均,造成局部温度在弯曲矫直时处于第Ⅲ脆性温度区;内部中心裂纹表面出现明显的液膜,在第Ⅰ脆性区凝固阶段产生。

Analysis of surface and internal defects for continuous casting billet of 82A tire cord steel

The surface crack defects and central segregation of cord steel are the key factors affecting the billet quality. The macro defect analysis on the surface of billet, micro morphology characterization of crack, Gleeble high temperature mechanical properties and central segregation measurements are applied, and the surface and internal quality defects of continuous casting 150 mm×150 mm billet of 82A cord steel under steady and unsteady state are analyzed. The results show that the distance between the vibration marks of the billet is 13 mm and the vibration marks at the corners are disordered. Obvious transverse cracks are observed at the vibration mark trough and pit on the surface of unsteady billet, but no transverse cracks are appeared in the steady-state samples. Moreover, an obvious central crack with a length of 55 mm along the central shrinkage cavity in the billet is found and the average central carbon segregation index of the billet is 1.09. Based on the analysis of high temperature mechanical and cracks morphology, the appearance of surface cracks is mainly related to the straightening in the low-temperature brittle zone due to uneven cooling under the unsteady condition, The local temperature is in the third brittle temperature zone during bending and straightening. An obvious liquid film appeared on the surface of the inner central crack, which was formed at the solidification stage of the first brittle zone.